Television



Oct. 30, 1934. H. J. MCCREARY TELEVISION Filed NOV. 9, 1928 HIGH TIME55c.

Patented Oct. 30, 1934 UNITED STATES TELEVISION Harold J. McCi-e'ary,Chicago, Ill., assignor, by mesne assignments, to Associated ElectricLaboratories, Inc., Chicago, 111., a

Delaware corporation of Application November 9, 1928, Serial No. 318,262

22 Claims.

The present invention relates in general to television and the object ofthe invention, broadly stated, is to provide a new and improvedtelevision receiver.

A special object of the invention is to provide a television receiver ofthe type which employs a cathode ray tube and which can be used to pickup television programs which are broadcasted by transmitting stationsusing the so-called disc w transmitter.

Other objects of the invention relate to various improvements intelevision receivers of the general character pointed out above and willbe discussed hereinafter.

Referring to the drawing accompanying this specification, Fig. 1 shows acathode ray television receiver using a neon tube oscillator forproducing the scanning potentials; Fig. 2 shows a modified type ofoscillator employing a motor-driven interrupting mechanism; Figs. 3 and4 show the wave forms of the scanning potentials which are produced bythe oscillators shown in Figs. 1 and 2; while Fig. 5 is a diagrammaticrepresentation showing how the television frame in the cathode rayreceiver of the instant case compares with the television frame in adisc type of receiver or transmitter.

Referring now to Fig. 1, the reference letter A refers generally to acathode ray tube of the general type which is in common use and known asa cathode ray oscillograph tube. It comprises an evacuated glass vesselor tube within which is a filament or cathode 2, a perforated disc orshield 3, an anode 4, and two pairs of plates 5-6 and '78. The end ofthe tube opposite the filament is preferably flattened out somewhat andis coat-.

ed on the inside with some fluorescent material, such as willemite. TheA" battery 10 is provided for the purpose of lighting the filament 2,while the so-called 13" battery 11 serves to place a positive potentialon the anode 4. A C battery 12 is also provided for the purpose ofmaintaining a negative potential upon the shield 3. In series with thebattery 12 is a high resistance grid leak 13. a

The reference letter B indicates generally the last stage of aresistance coupled amplifier. This amplifier may be any good type ofradio receiver such as is used topick up ordinary radio broadcasts. Theamplifier is coupled to the oathode ray receiver by means of condensers14 and 15.

The reference letter C indicates a double neon tube oscillator which isprovided for the purpose of impressing the necessary scanning potentialsupon the plates 5 to 8, inclusive, of the cathode ray receiver. The lowfrequency oscillator comprises essentially the neon tube 25 shunted byvariable condenser 27 and connected in series with the battery 31through the high resistance 29. The high frequency oscillator is similarand comprises the neon tube 26 shunted by variable condenser 28 andconnected in series with the same battery 31 through the high resistance30. The voltage of the battery 31 is variable so that the frequency ofthe oscillators can be adjusted. One end of the battery may be tappedfor rough adiustment, one cell at a time, while at the other end of thebattery a potentiometer is provided shunted around one or two of thecells to provide for a finer adjustment. The positive pole of thebattery is connected to common lead 42 which is connected to plates 5and 8 of the cathode ray receiver. The low frequency conductor 40 isconnected to scanning plate 6 of the receiver, while the high frequencyconductor 41 is con nected to the scanning plate '7. The common lead 42includes the potentiometer 33 which is shunted around the battery 32.This battery is connectedin opposition. to the battery 31 and isprovided so that the cathode ray beam can be centered on the fluorescentscreen 9 of the receiver. Battery 32, being connected in the commonlead, provides only for a diagonal adjustment across the screen, whichhowever, is ordinarily all that is required. Separate vertical andhorizontal adjustments can be provided for by inserting a potentiometerand battery in each of the leads 40 and 41, omitting the potentiometerand battery in the common lead 42.

The leads 40, 41, and 42 are connected to the receiver through keys K1,K2, and K3. Key K1 reverses the connections to the low frequencyscanningplates 5 and 6, while key K2 reverses the connections to thehigh frequency scanning plates '7 and 8. Key K3 reverses the high andlow frequency conductors 40 and 41 with respect vto their connections inthe receiver. These keys are provided so that any desired direction ofscanning may be secured.

Assuming that the receiver is set up and connected as shown in thedrawing, the filament 2 will be heated by the battery 10 and is thuscaused to emit electrons. In the ordinary operation of a cathode raytube of this type the potential on 105 the anode 4 is sumcient to pull astream of electrons through the central opening in the shield 3, thusforming the well-known cathode ray or beam which passes through thecylindrical anode 4 and between the pairs of plates 5-6 and 7-8 110andimpingesonthescreenDattheendofthe tube. The 6" battery 12 should havesuch a value that the negative potential on the shield 3 will verynearly prevent the e of anyelectrons when there is no incoming lightsignal; that is, with no incoming signal the cathode beam should be verynearly, if not quite, extinguished. m\n

The purpose of the two pairs of scan g plates 56 and 7-8 is, of course,to cause the cathode beam to scan or trace a path over the fluorescentscreen 9 so as to display the picture being received. This operation isdescribed in my co-pending application, Serial No. 705,413, filed April10, 1924, which describes the use of approximately sine wave generatorsfor producing the scanning potentials. When potentials having such awave form are used, however, the beam will trace a zig-zag or Lissajousfigure ori the fluorescent screen, and since this does not correspond tothe method of scanning used in the disc transmitter, potentials having adifferent wave form must be used. The foregoing may be understood betterby reference to Fig. 5. The dotted semi-rectangular frame abxurepresents the area scanned by a disc transmitter, horizontal clockwisescanning being assumed. The first hole in the disc will trace a pathacross the frame as represented by the dotted line ab, the second holewill trace a path represented by the dotted line dc, etc. It will beunderstood from this that the frame is scanned from top to bottom andfrom left to right, or the same as one reads a page of English print.The problem is to cause the cathode ray beam to scan the frame in thecathode ray receiver in the same manner. This can be done by arrangingfor. generation of scanning potentials having a wave form such as isillustrated in Figs. 3 and 4, Fig.

3 showing the wave form of the high frequency scanning potential, whileFig. 4 shows the wave form of the low frequency scanning potential. Itwill be seen that in each case the voltage rises with approximatelystraight-line characteristics to a maximum and then suddenly,practically instantaneously, falls to zero. It will be understood thatwhen the voltage across condenser 28,

for instance, is rising the voltage across the resistance 30 will befalling and vice versa, so that assuming positive values above the baseline the curve, Fig. 3, represents the wave form of the potential acrossthe condenser, while if negative values are assumed above the base linethe curve shows the wave form of the potentials across the resistance30.

The effect of these scanning potentials on the movement of the cathodebeam will readily be perceived. Considering the rectangular frame shownby the solid lines in Fig. 5, we will assume that the scanningpotentials both have a value of zero at a given instant and that at thispartic- 4 ular instant the beam impinges at the point a in the upperleft-hand comer of the frame, which will be true with the reversingswitches K1, K2, and K3 in a particular position. As the voltage of thehigh frequency source rises, the beam will be pulled across the frametoward the point-b, but at the same time the voltage of the lowfrequency source is rising also, with the result that the beam willgradually be deflected downward so that it actually traces a path asindicated by the line ac. When the point e is reached the voltage'of thehigh frequency source drops suddenly to zero with the result that thebeam instantly assumes a position at point (1 on the left of the screen,there being no visible path on the screen to denote the transition ofthe beam from c to d. The voltage of the high frequency source now risesgradually again with the result that the beam sweeps across the screenagain from left to right following the path indicated by the line deuntil when e is reached the voltage again drops to zero and the beaminstantly assumes its position at the leftof the screen at point 1.Thus, it will be seen that the beam traces lines from left to rightacross the screen, each line being a little lower down on the screenthan its predecessor, until finally on the last movement across theframe the beam arrives at the point 1!. At this instant the voltage ofthe low frequency source drops to zero simultaneously with the voltageof the high frequency source and the beam thereupon instantly resumesits position at a in the upper left-hand corner of the frame. Thus, thebeam has traversed the entire frame in a series of horizontal lines. Itwill be understood that the lines are much closer together in practicethan are shown in Fig. 5, as this drawing is merely for the purpose ofexplaining the principle, and the displacement of the lines ac, de,etc., from the horizontal will be much less than appears on the drawing.While these lines do not coincide exactly with the-lines 'ab, dc, etc.,the method of scanning is the same; that is, the cathode ray scans in aclockwise direction and from top to bottom, and the departure of thelines produced by the cathode ray beam from the paths followed by theholes in the disc is very small. It is so small as to produce merely avery slight distortion of the picture which is practically unno- 11oticeable. Y

The neon tube oscillator C is so designed as to produce scanningcurrents having the requisite wave form, as pointed out in theforegoing. The frequencies of the two oscillators must, of course,correspond to the picture frequencies employed at the transmittingstation whose broadcasted pictures it is desired to receive.Broadcasting stations are now in operation which transmit at the rate offifteen pictures per second using a disc having forty-eight holes. Toreceive these programs the low frequency oscillator including the neontube 25 must have a frequency of fifteen cycles persecond, while-thehigh frequency oscillator including the neon tube 26 must have afrequency of forty-eight times this or seven hundred twenty cycles persecond. The desired frequencies can be obtained by using the propervalues for the resistances 29 and 30 and for the condensers 2'1 and 28.It is desirable, however, that the resistances 29 and 30 both becomparatively high, on the order of 10 megohms, and it is preferable,therefore, to take care of the difference in frequencies largely bymeans of a difference in the capacities of the two condensers 27 and 28.It follows from this that the condenser 27 of the low frequencyoscillator will have a very much higher capacity than the condenser 28.The approximate values can readily be calculated from the formula inwhich f=frequency in cycles per second; E=charging potential in volts(battery 31); e=breakdown voltage of neon tube; R=resistance in ohms(resistance 29) and C=capacity in farads (condenser 27).

In the operation of the oscillator, and considering the low frequencyside, the condenser 27 will be charged by the battery 31 through theresistance 29 until the potential across the terminals 'of the condenserreaches the value at which the neon tube 25 flashes over. When thisoccurs, the condenser is short-circuited through the neon tube and isinstantly discharged. The neon tube then becomes open-circuited and thecondenser is again charged, the operation continuing in this manner atthe rate of fifteen cycles per second. The exact frequency can beadjusted by adjusting the condenser 2'7. The breakdown potential of theneon tube may be in the neighborhood of volts and the battery 31 shouldhave a voltage somewhat higher than this so that the condenser 27 willbe worked on the lower portion of its charging curve which has nearly astraight-line characteristic.

The high frequency oscillator including the neon tube 26, of course,operates the same as the low frequency oscillator except that thecondenser 28 charges and discharges exactly forty-eight times as fast asthe condenser 27. The exact frequency is adjusted by adjusting thecapacity of the variable condenser. When the two oscillators areseparately adjusted to substantially the proper frequencies they tend tokeep in step with each other, due to the inclusion of the resistance 35in the negative lead from the battery 31, and can then be adjustedsimultaneously by regulating the voltage of battery 31.

The high and low voltage leads 40 and 41 could be taken directly fromthe terminals of the condensers, if desired, common lead 42 beingconnected to the other terminal of the battery in this case, but it isbetter to connect these leads around the resistances 29 and 30 so thatthe oscillators will be independent of any extraneous circuits whichmight introduce variable capacity effects which would have a tendency tomake it difiicult to maintain adjustment of the frequencies. Theresistances 29 and 30 are preferably constructed in the form ofpotentiometers so that the impressed voltages on conductors 40 and 41can be varied for the purpose of varying the amplitude of movement ofthe cathode ray beam as it traverses the fluorescent screen in thereceiver. By adjusting the potentiometers toward the outside terminalsof the resistances the voltages on the conductors 40 and 41 will, ofcourse, be increased and the amplitude of the beam will be increasedalso. Thus the beam can be made to cover as large or small a frame as isdesired within the limits of the apparatus.

It will be understood now that with the oscillator in operation?connected up as shown the cathode ray bea in the receiver A will becaused to traverse a path across an imaginary picture frame such as isshown in Fig. 5 on the fluorescent screen 9 at the end of the tube,viewing the tube from the outside, or from the right of the drawing.With no incoming signal this frame will be practically invisible. Whenlight signals are received, however, the potential of the shield 3 willbe made more positive so that more electrons are permitted to passthrough, and the intensity of the beam is thus greatly increased, theamount of increase, of course, depending on the strength of the receivedsignal at any given instant. It follows, therefore, that as the beamtraverses the frame its intensity will change in accordance with thechange in the incoming light currents so that certain portions of theframe will be more or less brightly illumisystems of transmission.

nated while other portions of the frame will be left dark, all inaccordance with the illumination of the picture which is beingtransmitted.

The modified form of oscillator shown in Fig. 2 may be used in place ofthe neon tube oscillator in circumstances where a motor is available andwhere the use of moving parts is not objection able. The motor-drivenoscillator is somewhat simpler to operate than the neon tube oscillator,as there are less adjustments, but ordinarily it will not be asdesirable as the latter in which all moving or rotating parts of theordinary kind are eliminated. 7

Referring to the drawing, the reference letter M indicates the drivingmotor which may be a synchronous motor running in step with the motor atthe transmitting station or it may be an ordinary shunt field motorarranged to be adjusted by hand to the required speed, for instance 900R. P. M. On the shaft of the motor is mounted an interrupting mechanismwhich comprises the slip ring 52 and the short-circuiting commutators 51and 53. The slip ring 52 serves to connect the negative pole of thebattery 31' with the active segments of the two commutators. The brushof commutator 51 is connected to the far side of condenser 27' while thebrush of commutator 53 is connected to the far side of condenser 28'.The commutator 53 has one active segment while the commutator 51 hasforty-eight active segments. Assuming a motor speed of 900 R. P. M.,commutator 53 will shortcircuit the condenser 28 fifteen times persecond, while commutator 51 will short-circuit the condenser 27' sevenhundred twenty times per second. This produces the proper scanningfrequencies for receiving programs transmitted at the rate of fifteenpictures per second with a forty-eight-hole scanning disc. The apparatuscan, of course, be adjusted for other rates of transmission, although ifthe ratio between the number of pictures per second and the number ofholes in the scanning disc is different from that assumed, then one orboth of the commutators will have to be changed. The neon tubeoscillator possesses an advantage in this respect in that the frequencyof the oscillators can be independently adjusted and thus the samephysical apparatus can be used on a number of different The rest of theapparatus in. Fig. 2 is similar to the corresponding apparatus shown inFig. 1, except that the conductors 40', 41, and 42' are connected to thereceiver through condensers, which prevents displacement of the ray bythe battery 31', and renders it unnecessary to provide a compensatingbattery such as 32, Fig. 1. The condensers are indicated by referencecharacters 80, 81, and 82, and should be of large capacity, on the orderof 2 m. f. High resistance leaks 83 and-84 should also be used,connected from leads 40' and 41' to the common lead 42'. It will beunderstood that the condenser method of coupling can also beused withthe oscillator shown in Fig. 1.

Having described my invention, what I consider to be new and desire tohave protected by Letters Patent will be pointed out in the appendedclaims.

What is claimed is: 145

1. In a television receiver, a cathode ray device, said device includinga target and two pairs of deflecting plates, two sources of potentialconnected to said pairs of plates, respectively, to cause the beam toscan the target, and a-revers- 15,

ing switch included in said connections for reversing the direction ofscanning.

2. In a television receiver, a screen, means for.

producing a cathode ray, means for causing the ray to scan the screen ina series of disconnected lines, and means for changing the direction ofthe lines.

3. In a television receiver, a screen, means for producing a cathoderay, means for causing the ray to scan the screeen in a series ofdisconnected lines, and means for changing the order in whichconsecutive lines are produced on the screen.

4. In a television receiver, a cathode ray device, said device includinga target and beam deflecting plates, means for producing deflectingpotentials on said plates including a current source having one poleconductively connected to one or more of said plates, and an opposedcurrent source included in the conductive connection to aid in centeringthe beam on said target.

5. In a television "receiver, a cathode ray device, said deviceincluding a screen on which the ray impinges, an oscillator forproducing electrostatic fields to cause the ray to scan the screen, andadjustable means for causing the ray to scan any limited desiredfractional portion of said screen.

6. In a television receiver, a screen, means for producing a cathoderay, means for causing said ray to scan the screen in a series ofdisconnected lines, and means for reversing the direction of scanningand the order in which consecutive lines are produced on the screen.

7. In a television receiver, a screen, means for producing a cathoderay, means for causing said ray to scan the screen in a series ofdisconnected lines, and means for reversing the direction of scanningand for changing the direction of said lines.

8. In a television receiver, a screen, means for producing a cathoderay, means for causing said ray to scan the screen in aseries ofdisconnected lines, and means for changing the direction of said linesand the order in which consecutive lines are produced on the screen.

9. In a television receiver, a screen, means for producing a cathoderay, means for causing said ray to scan the screen in a series ofdisconnected lines, and means for changing the direction of said lines,for reversing the direction of scanning, and for changing the order inwhich consecutive lines are produced on the screen.

10. In a television receiver, a cathode ray device including a screenand two pairs of deflecting plates, two sources of potential connectedto said pairs of plates, respectively, to cause the beam to scan thetarget in a series of disconnected lines extending from left to right,said lines being produced consecutively from top to bottom, and meansfor changing said connections, so that said lines extend from right toleft.

11. In a television receiver, a cathode ray device including a screenand two pairs of deflecting plates, two sources of potential connectedto said pairs of plates, respectively, to cause the beam to scan thetarget in a series of disconnected lines extending from left to right,said lines being produced consecutively from top to bottom, and meansfor changing said connections so that said lines are producedconsecutively from bottom to top.

12. In a television receiver, a cathode ray device including a screenand two pairs of deflecting plates. two sources of potential connectedto said pairs of plates, respectively, to cause the beam to scan thetarget in a series of disconnected lines extending from left to right,said lines being produced consecutively from top to bottom, and meansfor changing said connections to cause the beam to scan-the target in aseries;, of disconnected lines extending from top to bottom, said linesbeing produced consecutively from left to right.

13. In a television receiver, a cathode ray device including a screenand two pairs of deflecting plates, two sources of potential connectedto said pairs of plates, respectively, to cause the beam to scan thetarget in a series of disconnected lines extending from left to right,said lines being produced consecutively from top to bottom, and meansfor changing said connections to cause the beam to scan the target in aseries of disconnected lines extending from bottom to top, said linesbeing produced consecutively from right to left.

14. In a television receiver, a cathode ray device including a targetand two pairs of beam deflecting plates, means for producing deflectingpotentials on said plates, said means including a source of currenthaving one pole conductively connected to one plate in each of saidpairs, and adjustable means included in said connection for varying thepotential on the two connected plates so that the point of impact ofsaid beam may be shifted diagonally across said target.

15. In a television receiver, a cathode ray device including a screenand two pairs of beam deflecting plates, a source of potential connectedin multiple to one plate in each pair, an oscillator for producing twofluctuating potentials connected to the other two plates, respectively,to produce deflections of the beam to cause it to scan said screen, andmeans for causing said beam to scan any desired portion of said screen,said means including adjustable means in said common connection forshifting the point of im-- pact of said beam diagonally across saidscreen and adjustable means in each of said individual connections forvarying the amplitudes of the deflections of said beam.

16. In a television receiver, a cathode ray device including a screenand two pairs of beam deflecting plates, a neon tube oscillator forproducing high and low frequency scanning potentials of a wave formhaving a substantially vertical component on one side, a common leadfrom said oscillator to one plate in each pair, a biasing battery insaid common lead for normally maintaining the beam in contact with onecorner of said screen, a low frequency output lead from said oscillatorconnected to the other plate of one of said pairs for slowly deflectingsaid beam in one direction across said screen, and a high frequencyoutput lead from said oscillator connected to the other plate in theother pair for rapidly deflecting said beam across said screen in adirection at right angles to said first direction.

1'7. In a television receiver, a cathode ray device including a screenand two pairs of beam deflecting plates, a differential oscillatorcomprising two neon tube oscillating circuits coupled by a common branchincluding a source of current, means for adjusting the frequency of eachoscillating circuit separately, a resistance in said common branch forcausing said oscillating circuits to tend to keep in step whenoscillating at multiple frequencies, and connections from saidoscillator to sai d deflecting plates such that said beam is caused toscan said screen in a series 01' disconnected lines.

18. In a television receiver, a cathode ray device including a screenand two pairs of beam deflecting plates, a differential oscillatorcomprising two oscillating circuits each including a resistance and aneon tubeshunted by a condenser connected in series with a source ofcurrent common to both circuits, and connections from said oscillator tosaid deflecting plates such that the beam is caused to scan said screenin a series of disconnected lines, said connections including a multipleconnection from one pole of said current source to one plate in eachpair and adjustable connections from said resistances to the other twoplates, respectively.

' 19.- In a television receiver, a cathode ray device including a screenand two pairs of beam deflecting plates, an oscillator comprising twoneon tube oscillating circuits coupled by a common branch including asource of current, means for adjusting. each circuit separately so thatone oscillates at a frequency'having a definite multiple relationship tothe frequency of the other, connections from said oscillator to saiddeflecting I plates such that the beam is caused to scan the is causedto scan said screen in a series of disconnected lines, means foradjusting the irequency of each oscillating circuit separately so thatthe two frequencies have a deflnite multiple relationship governed bythe mtmber of holes in the transmitting disc, means in said commonbranch for simultaneously adjusting said frequencies to correspond tothe speed of rotation' of the disc at the transmitting station, andmeans for maintaining said multiple relationship between saidfrequencies during said adjustment.

21. In a television receiver, a screen, means for producing a cathoderay impinging on said screen, two pairs of deflecting plates, means forimpressing on each pair of plates successive potentials of only onepolarity, thereby causing movement of the ray in two directions fromnormal, and means for impressing on said pairs of plates a constantpotential of opposite polarity to alter the normal position of said rayfrom which said movements begin.

22. In a television receiver, a screen, means for producing a cathoderay which normally impinges on said screen at a flxed point, two pairsof deflecting plates, means for impressing varying potentials of onlyone polarity but of two different frequencies on said pairs of plates,respectively, to cause the ray to scan a rectangular area on said screenextending in two directions from said fixed point, and means common toboth pairs of plates for placing a constant-biasing potential on saidplates to shift the point at which the ray impinges on the screen,whereby the deflecting potentials cause the my to scan a rectangulararea on a different portion of said screen.

HAROLD J. MCCREARY.

